Q & A: Understanding the Discovery

1.
How does Hubbleís view compare with that of Deep Impact?

The observations by the Deep Impact camera and the Hubble telescope complement each other. The camera aboard the Deep Impact spacecraft will provide a close-up view of the comet, from more than 300 miles away. The Hubble telescope, from its distance 80 million miles away, will capture a wider view of the encounter. The difference between the views from Hubble and the Deep Impact spacecraft is like that between a satellite image of a hurricane and a photo from the center of the storm. Hubble also will continue to monitor the comet's activities for several days after the event.

2.
Why is it important to probe a cometís interior?

"This is like opening a time capsule," said Paul Feldman, professor of physics and astronomy at the Johns Hopkins University in Baltimore, Md. "Some of the material near the comet's surface is released as the comet is blasted by the Sun's heat each time it makes its rounds through the solar system. But the NASA Deep Impact mission is like forcibly taking a can opener to the comet. This is our first view deep inside the heart of a comet. We hope this event will give us information on this comet's makeup and will open a window onto our early solar system."

3.
How difficult is it for Hubble to track the comet?

Hubble had a difficult task in following the small comet. The telescope had to track the speedy comet like a photographer taking pictures of a car race. The Advanced Camera for Surveys' high-resolution camera snaps an image a minute for 10 to 15 minutes before the telescope's view was blocked as it circled Earth.

4.
Why canít Hubble see the cometís nucleus?

Tempel 1's nucleus, a potato-shaped object that is 8.7 miles (14 kilometers) wide and 2.5 miles (4 kilometers) long, is so small and so far away that even the Hubble telescope can not see it. The telescope did see the inner cloud of dust and gas enshrouding the nucleus. Spotting the Tempel 1 nucleus was as difficult as seeing a potato in Salt Lake City from a distance as far away as New York City. "Hubble is critical to this mission," Feldman said. "When the mission planners selected an impact time, they made sure that Hubble would be able to see the event."

5.
Is Hubble just taking pictures?

Besides hopefully witnessing the crash, Hubble will also monitor the plume of debris kicked up from the impact. "Some of the gases expected to be released, such as carbon monoxide, carbon, and sulfur, can best be seen in ultraviolet light," Feldman explained. These gases come from ices that condensed out of the cloud of material from which the solar system formed and are part of the makeup of all comets.

Hubble will study the expected plume of dust and gas that may be ejected from the surface of the comet and from below its surface as a result of the impact. By analyzing the Hubble observations, astronomers will determine the speed of the ejected material, how far the plume extends into space, and something about its chemical makeup. Hubble's observations will include images taken in visible light, as well as images and spectra taken in ultraviolet light. Some of the gases expected to be released, such as carbon monoxide, carbon, and sulfur, can best be seen in ultraviolet light. These gases come from ices that condensed out of the cloud of material from which the solar system formed.

6.
What are comets?

Comets are thought to be "dirty snowballs," porous agglomerations of ice and rock that dwell in the frigid outer boundaries of our solar system. Periodically, they make their journey into the inner solar system as they loop around the Sun. Comets are relics of our early solar system, chunks of leftover material from the formation of the planets. Locked beneath the comet's surface is pristine material that astronomers want to study to learn how our solar system formed.